php连接mysql 预处理

<?php
try {
    // 创建PDO实例
    $pdo = new PDO('mysql:host=localhost;dbname=testdb', 'username', 'password');
    $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

    // 准备SQL语句
    $stmt = $pdo->prepare('SELECT * FROM users WHERE username = :username AND password = :password');

    // 绑定参数
    $stmt->bindParam(':username', $username);
    $stmt->bindParam(':password', $password);

    // 设置参数值
    $username = 'admin';
    $password = 'password';

    // 执行查询
    $stmt->execute();

    // 获取结果
    $result = $stmt->fetchAll(PDO::FETCH_ASSOC);

    // 输出结果
    print_r($result);
} catch (PDOException $e) {
    echo 'Connection failed: ' . $e->getMessage();
}
?>

$pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);